How do I get the name of captured groups in a C# Regex?

Use GetGroupNames to get the list of groups in an expression and then iterate over those, using the names as keys into the groups collection.

For example,

GroupCollection groups = regex.Match(line).Groups;

foreach (string groupName in regex.GetGroupNames())
{
    Console.WriteLine(
       "Group: {0}, Value: {1}",
       groupName,
       groups[groupName].Value);
}

The cleanest way to do this is by using this extension method:

public static class MyExtensionMethods
{
    public static Dictionary<string, string> MatchNamedCaptures(this Regex regex, string input)
    {
        var namedCaptureDictionary = new Dictionary<string, string>();
        GroupCollection groups = regex.Match(input).Groups;
        string [] groupNames = regex.GetGroupNames();
        foreach (string groupName in groupNames)
            if (groups[groupName].Captures.Count > 0)
                namedCaptureDictionary.Add(groupName,groups[groupName].Value);
        return namedCaptureDictionary;
    }
}

Once this extension method is in place, you can get names and values like this:

    var regex = new Regex(@"(?<year>[\d]+)\|(?<month>[\d]+)\|(?<day>[\d]+)");
    var namedCaptures = regex.MatchNamedCaptures(wikiDate);

    string s = "";
    foreach (var item in namedCaptures)
    {
        s += item.Key + ": " + item.Value + "\r\n";
    }

    s += namedCaptures["year"];
    s += namedCaptures["month"];
    s += namedCaptures["day"];

Since .NET 4.7, there is Group.Name property available.